1. Field of the Invention
This invention relates generally to electrical circuits for providing operating signals to electro-optic devices in a photonic integrated circuit and, more particularly, to arrays of such electrical circuits to provide such operating signals to corresponding arrays of optical devices. Preferably the electrical circuits are provided on a single substrate.
2. Description of the Related Art
Optical circuits, and the corresponding electrical circuits which support such optical circuits, have become commonplace in the formation of a digital network infrastructure utilized for data transport as the need for increased network carrying capacity continues to grow. Such optical circuits, for example, may include arrays of optical signal paths, each signal path having multiple electro-optic devices including, but not limited to, laser sources, modulated laser sources, modulators, amplifiers, attenuators, and monitoring devices, all preferably provided on a common substrate. Examples of such photonic integrated circuits can be found in U.S. Pat. No. 7,283,694, entitled “TRANSMITTER PHOTONIC INTEGRATED CIRCUITS (TXPIC) AND OPTICAL TRANSPORT NETWORKS EMPLOYING TXPICS,” and U.S. Pat. No. 7,116,851, entitled “AN OPTICAL SIGNAL RECEIVER, AN ASSOCIATED PHOTONIC INTEGRATED CIRCUIT (RxPIC), AND METHOD IMPROVING PERFORMANCE,” both of which are incorporated herein in their entirety by reference.
Due to certain systematic performance variations of such monolithic photonic integrated circuits, optical signals output from photonic integrated circuits may have undesirable optical characteristics. Certain remedies for such variations relative to photonic integrated circuits can be found in copending U.S. patent application Ser. No. 12/263,471, entitled “PHOTONIC INTEGRATED CIRCUITS HAVING CHIRPED ELEMENTS,” sharing a common assignee with the present application, the application incorporated herein in its entirety by reference.
One typical electro-optic device in each optical signal path is an optical modulator, which modulates the optical signal in the signal path in response to a received control signal, typically referred to as a bias signal or modulator drive signal. Generally, a modulator driver circuit is coupled to the modulator and accepts a data signal as an input, e.g. a data signal carrying information to be transmitted over a network infrastructure. The modulator driver circuit, in turn, generates an output modulator drive signal to be provided to the modulator, e.g. a Mach Zehnder modulator (MZM) or a semiconductor electro-absorption modulator (EAM). In response to the output modulator drive signal the modulator then modulates the optical signal propagating in the optical signal path to facilitate optical transmission of the data signal across the network infrastructure. Notwithstanding those remedies discussed in U.S. patent application Ser. No. 12/263,471, supra, each modulator of each of the optical signal paths may require a slightly different modulation drive signal in order to provide proper modulation. While discrete modulator driver circuits can be fabricated, each specifically tailored to a particular modulator, such discrete circuits are costly and complex.
Accordingly, there is a need for a modulator driver circuit which has a simplified design that provides an improved modulator drive signal. Additionally, what is needed is an array of such modulator driver circuits, each modulator driver circuit comprising one or more electrical components, each having one or more parameters which are varied across the array of modulator driver circuits to provide a corresponding array of desired modulator drive output signals. Such an array of modulator driver circuits are preferably provided on a common substrate.